.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" %%%LICENSE_END
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2001-04-01 by aeb
.\" Modified 2003-07-23 by aeb
.\"
.TH USLEEP 3  2016-03-15 "" "Linux Programmer's Manual"
.SH NAME
usleep \- suspend execution for microsecond intervals
.SH SYNOPSIS
.nf
.B "#include <unistd.h>"
.sp
.BI "int usleep(useconds_t " usec );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR usleep ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.12:
.nf
(_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
    || /* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.TP 4
.fi
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.PD
.RE
.ad b
.SH DESCRIPTION
The
.BR usleep ()
function suspends execution of the calling thread for
(at least) \fIusec\fP microseconds.
The sleep may be lengthened slightly
by any system activity or by the time spent processing the call or by the
granularity of system timers.
.SH RETURN VALUE
The
.BR usleep ()
function returns 0 on success.
On error, \-1 is returned, with
.I errno
set to indicate the cause of the error.
.SH ERRORS
.TP
.B EINTR
Interrupted by a signal; see
.BR signal (7).
.TP
.B EINVAL
\fIusec\fP is not smaller than 1000000.
(On systems where that is considered an error.)
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR usleep ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
4.3BSD, POSIX.1-2001.
POSIX.1-2001 declares this function obsolete; use
.BR nanosleep (2)
instead.
POSIX.1-2008 removes the specification of
.BR usleep ().

On the original BSD implementation,
and in glibc before version 2.2.2, the return type of this function is
.IR void .
The POSIX version returns
.IR int ,
and this is also the prototype used since glibc 2.2.2.

Only the
.B EINVAL
error return is documented by SUSv2 and POSIX.1-2001.
.SH NOTES
The type
.I useconds_t
is an unsigned integer type capable of holding integers
in the range [0,1000000].
Programs will be more portable
if they never mention this type explicitly.
Use
.in +4n
.nf
.sp
#include <unistd.h>
\&...
    unsigned int usecs;
\&...
    usleep(usecs);
.fi
.in
.LP
The interaction of this function with the
.B SIGALRM
signal, and with other timer functions such as
.BR alarm (2),
.BR sleep (3),
.BR nanosleep (2),
.BR setitimer (2),
.BR timer_create (2),
.BR timer_delete (2),
.BR timer_getoverrun (2),
.BR timer_gettime (2),
.BR timer_settime (2),
.BR ualarm (3)
is unspecified.
.SH SEE ALSO
.BR alarm (2),
.BR getitimer (2),
.BR nanosleep (2),
.BR select (2),
.BR setitimer (2),
.BR sleep (3),
.BR ualarm (3),
.BR time (7)
